Hi,
Not sure, but it sounds like one of his own compositions. Here is a link to his discography website, and you might be able to identify the tune if you scroll through all of the numbers in it.
http://ludovicbeier.com/#/discographie/3304326
Hes possibly the biggest name accordionist in France, and what is very pleasant is that although he is one of the new generation he plays in a traditional style. His repertoire is heavy on jazz and gypsy (manouche), but as he aptly demonstrates with this clip, he is no slouch in the valse musette genre either.
Im tempted to say dont try this at home, even if if you manage to identify the tune and get the sheet music. Ludovic Beier is literally one in a million, and I would reckon it would take another accordionist in a million to be able to play like he does. Mind you it was older generation players who played in a similar style to him, who persuaded me away from the full three voice musette into the world of bassoon reeds in tone chambers, and very expensive accordions. Problem is that the fancy accordion never made me a better player, but I still get a lot of pleasure out of kidding myself that I may have been a top player if Id started younger.
The You Tube posting was made by Benny Hennebel, whose late father, Albert, was a top Belgian accordionist from West Vlaanderen, just over the border from Dunkirk.
Hope you manage to identify the tune, and good luck if you try learning it. I like the tune a lot, but Ill leave Mr Beier to play it, as I reckon he makes a slightly better job of it than I could!